2-methylbut-3-yn-2-ol

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-methylbut-3-yn-2-ol

EC Number:

204-070-5

EC Name:

2-methylbut-3-yn-2-ol

Cas Number:

115-19-5

Molecular formula:

C5H8O

IUPAC Name:

2-methylbut-3-yn-2-ol

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

90 days

Frequency of treatment:

once daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

45 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

130 mg/kg bw/day (nominal)

Doses / concentrations 3

Dose / conc.:

400 mg/kg bw/day (nominal)

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

In all male and all female animals of test group 3 (400 mg/kg bw/d) slight unsteady gait was observed on several days of the study within 2 hours as well as within 2 to 5 hours after administration. The sign was observed first in males on study day 12 and in females on study day 10. Reduced attention was observed in all males and 7/10 females (Nos. 71-76 and 79) of the same test group on several days of the study within 2 hours as well as within 2 to 5 hours after administration. This finding was seen first in males on study day 16 and in females on study day 31. Additionally, in 6/10 male (Nos. 31, 33, 34, 38-40) and 5/10 female (Nos. 72-76) high dose group animals semiclosed eyelids of both eyes was observed within 2 to 5 hours after administration starting on study day 55 in males and on study day 31 in females. Furthermore, in all male and all female animals of test group 2 (130 mg/kg bw/d) slight unsteady gait was observed on several days of the study within 2 hours (except male No. 28 and female No. 64) as well as within 2 to 5 hours after administration. The sign was seen first in in both sexes on study day 37. All animals of test groups 2 and 3 (130 and 400 mg/kg bw/d) recovered from all above mentioned findings overnight. None of the listed findings above had been observed on the next day before treatment. In 1 female (No.58) of test group 1 (45 mg/kg bw/d) slight poor general condition, piloerection and pale skin on entire body was observed within 2 hours as well as within 2 to 5 hours after administration on study day 10. The animal recovered overnight. These unique appearing findings are assessed as incidental and spontaneous in nature and not related to treatment. No clinical findings were observed in male of test groups 1 (45 mg/kg bw/d).

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

no effects observed

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

From beginning of determination (study day 25) until end of administration period water consumption was increased in male animals of test group 3 (400 mg/kg bw/d) with an increase >20% between study days 53-56, 60-63, and 81-84 as well as in males of test group 2 (130 mg/kg bw/d) with an increase >20% between study days 39-42, 46-49, 53-56, and 60-63. In male animals of test group 1 (45 mg/kg bw/d) and in female animals of all test groups water consumption was not increased above 20%.

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of the administration period in males of test groups 2 and 3 (130 and 400 mg/kg bw/d) hematocrit values were significantly decreased. Additionally, in males of both mentioned test groups and of test group 1 (45 mg/kg bw/d) red blood cell (RBC) counts were significantly decreased and relative reticulocyte counts, mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) content were significantly increased. Hematocrit values, MCH and relative reticulocyte counts in males of test groups 1 and 2 were within historical control ranges (males hematocrit 0.410-0.448 L/L, MCH 1.00-1.09 fmol, relative reticulocytes 1.5-1.9 %). RBC counts and MCV in males of test group 1 were also within the historical controls range whereas those of test group 2 were marginally outside these ranges (males RBC 8.31-9.08 Tera/L, MCV 47.8-51.1 fL). MCV is a calculated index using the measured red blood cell parameters hematocrit and RBC counts, the first parameter within, the last one marginally below the historical control range in males of test group 2. Therefore, red blood cell parameter changes in males of test group 1 and 2 (45 and 130 mg/kg bw/d) were regarded as treatment related but not adverse, because none or at maximum one measured parameter (RBC counts in test group 2) were outside historical control ranges (ECETOC Technical Report No 85, 2002). Several red blood cell parameters in males of test group 3 (400 mg/kg bw/d) were clearly outside the historical control ranges and therefore, these changes were regarded as adverse.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of the administration period in rats of both sexes of test group 3 (400 mg/kg bw/d), alanine aminotransferase (ALT) activities were significantly higher compared to controls. Additionally, in males of test group 1 and 3 (45 and 400 mg/kg bw/d) aspartate aminotransferase (AST) activities were significantly increased. However, the higher AST values in test group 1 were not dose dependently changed and were therefore, regarded as incidental and not treatment-related. The ALT and AST activity means in test group 3 were less than twofold higher compared to those of the study controls. Therefore, these alterations were regarded as treatment-related but not adverse (Hall et al., 2012).

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

No treatment-related changes among urinalysis parameters were observed. However, in rats of both sexes of test group 3 (400 mg/kg bw/d) urine volume was significantly higher compared to controls. This observation per se without any other finding in the urinary tract were regarded as treatment-related but not adverse. In males of test group 3 (400 mg/kg bw/d) significantly higher incidences of oxalate crystals were found in the urine sediment.

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

In the functional observation battery performed within 5 hours after treatment, slight impairment of coordination was observed manifested in the unsteady gait, food splay test, and grip strength in test group 3 (400 mg/kg bw/d) and partially in test group 2 (130 mg/kg). Additionally, a reduced motor activity was determined in the test group 3 within 8 hours after treatment. These findings were assessed as clinical pattern of a hypnotic chemical. The test substance is an alcohol with a tertian hydroxyl group with known hypnotic potential (Sehring K 1955). Therefore, these findings were assessed as treatment-related but not adverse.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

When compared with control group 0 (=100%), the absolute weights of the following organs were significantly increased or decreased in one or more test groups:
adrenal glands, brain, heart, kidneys, liver, ovaries, pituitary gland. All other mean absolute weight parameters did not show significant differences when compared to the control group 0.
When compared with control group 0 (=100%), the relative weights of the following organs were significantly increased or decreased in one or more test groups:
adrenal glands, epididymides, heart, kidneys, liver, ovaries, pituitary gland, thyroid glands. All other mean relative weight parameters did not show significant differences when compared to the control group 0.

The decreased mean relative epididymides weight in test group 3 males was regarded as treatment-related as it was below historical controls (historical controls: 0.301-0.322%, this study test group 3 0.276%).

Increased absolute and relative kidney weights of males of test groups 2 and 3 were regarded as treatment-related as there were both a macroscopic and a histological correlate. In test group 1, absolute kidney weights were within historical control values and relative weights were even below historical controls and therefore assessed as incidental (historical control:absolute weights: 2.138-2.320 g, relative weights 0.652-0.721%; male test group 1: absolute 2.24 g, relative 0.591%). Both, absolute and relative weights of the kidney in test group 3 female animals were above historical controls and therefore assessed as treatment-related (historical control: absolute weights: 1.388-1.619 g, relative weights 0.652-0.721; test group 3: absolute 1.653 g, relative 0.734%).

Increased absolute and relative liver weights of test group 3 male animals were regarded as treatment-related as they were above historical controls (historical control: absolute weights 7.611-8.493 g, relative weights 2.11-2.299; test group 3: absolute 9.124 g, relative 2.388%).

The decreased absolute and relative pituitary gland weights in female animals of test group 3 were assumed to be treatment-related as they were below historical controls (historical control: absolute weights 10.8-14.4 mg, relative weights 0.005-0.006%; test group 3: absolute 9.6 mg, relative 0.004%).

The absolute weights of the adrenal glands were increased in males of test group 3, however, no statistically significant changes were present in relative organ weights nor was there a histopathological correlate, therefore the increased absolute weights were considered to be incidental. The absolute and relative weights of the adrenals were decreased in females of test group 3, as there was no histopathological correlate, this was assessed as incidental.

The decreased brain weights of female test group 3 animals were regarded as incidental as no changes in relative weights were noted they were possibly due to increased terminal body weights in this group.

The slightly increased absolute heart weights of test group 3 males were regarded to be incidental as absolute weights were within historical controls, relative weights were minimally higher than historical controls but showed no dose-response relationship and there was no histopathological correlate (historical controls: absolute weights: 1.033-1.162 g, relative weights: 0.248-0.277%; test group 3: absolute 1.097 g, relative 0.286%). The minimally decreased relative heart weight of test group 1 females was still within historical controls and assessed as incidental (historical controls: 0.316-0.377%, this study test group 1 0.317%).

The increased absolute and relative weights of the ovaries in test group 1 and 2 females were assessed as incidental as there was no dose response relationship, (test group 3 weights were not significantly changed) and controls were below historical control (historical control: absolute weights 97.2-113.8 mg, relative weights 0.045-0.051%; test group 0: absolute 90.7 mg, relative 0.041%).

Decreased relative weights of the thyroid glands of both test group 2 and 3 males were regarded as incidental as absolute and relative weights were within historical controls (historical control: absolute weights 18.4-26.7 mg, relative weights 0.005-0.007%; test group 2: absolute 20.4 mg, relative 0.005%; test group 3: absolute 19.9 mg, relative 0.005%).

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Treatment-related findings were noted in the kidneys of male animals only. All other findings occurred either individually or were biologically equally distributed over control and treatment groups. They were considered to be incidental or spontaneous in origin
and without any relation to treatment.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Treatment-related findings were observed in kidneys and testes of male animals and in ovaries of female animals.
In males of test groups 2 and 3, eosinophilic droplets were noted with treatment-relatedly increased severity in proximal tubules of the kidney. Macroscopic findings of enlargement and discoloration correlated with the histopathological findings in test group 2 and 3. A histopathological correlate for the enlarged kidneys in two test group 1 males and in animal 40 (test group 3, which showed only minimal findings histopathologically) could not be detected. In 5 males of test group 3, minimal retention of spermatids was noted, characterized by two generations of elongated spermatids in tubules of stages X to XII, it was graded minimal, as only a few spermatids of step 19 were present (the mature form, which should have been released in stage VIII). In all females of test group 3, minimal to slight (micro)vacuolation of interstitial glands was observed. No morphological correlates were seen for the increased liver weights in test group 3 males and the decreased pituitary gland weights in test group 3 females.
All other findings occurred either individually or were biologically equally distributed over control and treatment groups. They were considered to be incidental or spontaneous in origin and without any relation to treatment.

Histopathological findings: neoplastic:

no effects observed

Other effects:

effects observed, treatment-related

Description (incidence and severity):

In males of test groups 1, 2 and 3 (45, 130 and 400 mg/kg bw/d), total sperm counts in the cauda epididymidis were significantly lower compared to controls. However, all values were within the historical control range (TS/gC 381-890 Mio/g) and the change was not dose dependent. Additionally, the percentage of abnormal sperms was statistically increased in males of test group 3 (400 mg/kg bw/d), with the dominating observation of an abnormal hook or a missing head. Abnormal sperm counts were already higher in males of test group 2 (130 mg/kg bw/d), but the change was not statistically significant and the mean was within the historical control range (abnormal sperms 6.0-7.2 %). Therefore, the combination of reduced sperm head counts and increased abnormal sperm counts in males of test group 3 (400 mg/kg bw/d) were regarded as adverse. In males of test group 2 (130 mg/kg bw/d) abnormal sperm head counts were not statistically significantly increased and both mentioned parameters were within historical control ranges. In test group 1 (40 mg/kg bw/d) only total sperm head counts were decreased, but the values were also within the historical control range. Therefore, the mentioned altered sperm parameters in males of test group 1 and 2 were regarded as incidental and not treatment-related. Concerning motility of the sperms and the sperm head counts in the testis no treatment-related effects were observed.

Significant test substance-related increase of estrous cycle length (6.5 days) and decrease of the number of cycles (2.3) were obtained in female animals of test group 3 (400 mg/kg bw/d). Female No. 77 of this test group had no complete estrous cycle during the observation period, thus mean cycle length could be determined in 9 of 10 females of test group 3 (400 mg/kg bw/d), only. No test substance-related effects on estrous cycle length and the number of cycles were obtained in female animals of test groups 1 and 2 (45 and 130 mg/kg bw/d).

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

45 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

gross pathology

histopathology: non-neoplastic

organ weights and organ / body weight ratios

2

Dose descriptor:

NOAEL

Effect level:

130 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical biochemistry

clinical signs

histopathology: non-neoplastic

organ weights and organ / body weight ratios

urinalysis

Target system / organ toxicity

Critical effects observed:

yes

Lowest effective dose / conc.:

130 mg/kg bw/day (nominal)

System:

urinary

Organ:

kidney

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

no

Applicant's summary and conclusion

Conclusions:

The administration of 2-methylbut-3-yn-2-ol by gavage to male and female Wistar rats for 3 months caused signs of systemic toxicity manifested on kidney as well as reproductive organs epididymis, testis, and ovary. These findings had been observed largely in the highest dose level tested (400 mg/kg bw/d). However, findings in the kidney of the male animals (macroscopic: enlarged and discolored, histological correlate: increased eosinophilic droplets) were also partially present at mid dose levels (130 mg/kg bw/d). Therefore, under the conditions of the study the no observed adverse effect level (NOAEL) was 45 mg/kg bw/d for male Wistar rats (NOAEL for female Wistar rats = 130 mg/kg bw/d).